Recent data insufficient for disaster prevention

By Hung Chih-Wen 洪致文

In the past few years, “global warming” and “climate change” have become fashionable scientific terms and “carbon reduction” and “disaster prevention” have become popular government slogans, but have we really sat down to review Taiwan’s climate conditions over the past century to understand the country’s true natural rhythm and considered how to face these severe natural challenges?

Indeed, whenever torrential rains cause major disasters, we immediately call it a natural disaster over which we have no control. Blaming “climate change” seems to have become a convenient excuse rather than accepting that it might have been caused by a failure to prepare adequately for disasters.

Under the Taiwan Climate Change Projection and Information Platform Project (TCCIP) promoted by the National Science Council, we have compiled rainfall data for Taiwan dating back more than a century. By integrating data from more than 1,000 observation stations, a TCCIP Taiwan Rainfall Index has been set up. This index highlights certain characteristics about the long-term variability of Taiwan’s rainfall that had previously been overlooked.

The analysis confirmed that there has been a change in Taiwan’s annual rainfall over this period. In general, there was higher precipitation during the middle and late period of the Japanese colonial era and into the early post-colonial period — basically from the 1930s until the 1960s — and then lower precipitation when Taiwan’s economy was taking off — between the 1960s and the 1990s. After the mid and late-1990s and especially after 2000, precipitation has increased again. Such long-term tendencies are shown in annual rainfall as well as the occurrence of “extreme rainfall events.”

In the past, government flood prevention schemes have been largely based on the calculation of annual rainfall over the past 20 to 30 years. Without considering the changing climate, the government has made once-in-a-century flooding projections based on only 30 years of observations. However, in the past decade or so, we have experienced repeated disasters caused by torrential rains. Statistically, such incidents are looked upon as statistical outliers beyond our control, but the fact is that if these outlier events occur frequently, and if they have also occurred frequently in the past, then this is a reflection of the true natural rainfall.

We should pay attention to the fact that the lower rainfall between the 1960s and the 1990s coincided with rapid population growth, a quickly expanding economy and urban expansion. Because precipitation dropped during this period, the government and the public gradually lost their alertness to floods and natural threats and began developing flood basins and rivers that had been left undeveloped during the rainier Japanese colonial era. With the increase in rainfall in the past decade, post-war land use, river development, dike construction, water resource management and so on endanger people’s lives and assets.

Historical data tell us that climate conditions are cyclical, with wet and dry periods alternating every few decades. If we plan our prevention measures according to the conditions in a relatively dry period, problems are likely to occur during wetter periods. Taiwan has had access to abundant meteorological observation data since the Japanese colonization era, but the Central Weather Bureau still has a lot of paper-based data that have not yet been digitized and analyzed due to lack of funds.